Motor vehicle emissions are governed by legal limits whose purpose is to minimize the environmental effects of motor vehicle traffic. This relates in particular to the emission of fine dust such as soot particles, and of nitrous oxides. A widespread approach for minimizing the emission of nitrous oxides provides for mixing part of the exhaust gas, produced during combustion of the fuel in the internal combustion engine, to the combustion air for the internal combustion engine, in order to thus lower the combustion temperature and to carry out the combustion of the fuel without excess oxygen. This technique, known as exhaust-gas recirculation (EGR), can conventionally be performed at high or low pressure, that is to say upstream (high-pressure EGR) or downstream (low-pressure EGR) of an exhaust-gas turbine and/or exhaust-gas aftertreatment devices. It is also possible to provide combinations of high-pressure and low-pressure EGR.
For exhaust-gas recirculation, exhaust gas is taken from the exhaust-gas stream of the internal combustion engine by a branch line and is mixed with the fresh air by means of an EGR valve, thus producing the combustion air for the internal combustion engine. It is then commonly possible to use the EGR valve to influence the mixing ratio of fresh air to exhaust gas, in order to permit suitable mixing ratios for various driving states. For example, it can be provided to interrupt the recirculation of exhaust gas in the case of very high engine power, because in this case a large quantity of fuel is burned and as much oxygen as possible is to be supplied with the combustion air. It can however also be provided, in the case of low engine power, to admix a large fraction of exhaust gas in order to burn the fuel without excess oxygen.
The invention has the object of introducing an improved low-pressure EGR valve.
The invention introduces a low-pressure EGR valve that is equipped with a fresh air inlet, an exhaust-gas outlet and an outlet. According to the invention, an internal wall of a housing of the low-pressure EGR valve between the outlet and the fresh air inlet has, at a lowest point during proper use of the low-pressure EGR valve, a drain for condensate.
The outlet of the low-pressure EGR valve is designed to be connected to a compressor which compresses, for the internal combustion engine, the combustion air prepared from the fresh air and the recirculated exhaust gas in variable mixing ratios.
In particular at low ambient temperatures, the water vapor contained in the recirculated exhaust gas can condense as a consequence of the cooling on contact with the fresh air supplied in the low-pressure EGR valve through the fresh air inlet, or by contact with the cold wall of the low-pressure EGR valve. The condensed water collects in the low-pressure EGR valve and can even freeze in the event of prolonged residence in the low-pressure EGR valve. The compressor, connected to the outlet in proper use of the low-pressure EGR valve, contains a compressor wheel that rotates at very high speed and sucks in the recirculated exhaust gas and the fresh air. The invention is based on and incorporates the knowledge that the compressor wheel can be damaged if water droplets or even ice particles are sucked in and impact on the compressor wheel. The low-pressure EGR valve of the invention has the advantage that condensed water can flow out of the low-pressure EGR valve through the drain. The water can then for example be removed via the exhaust-gas path and released into the environment. In that context, the drain represents a path for the condensate which is open even if the exhaust-gas inlet were closed for the condensate, for example because no exhaust gas is to be recirculated due to the instantaneous operating state.
Proper use is to be understood here as meaning that the low-pressure EGR valve is installed in a motor vehicle and the motor vehicle is arranged on a flat road. Preferably, the connection face is formed such that, under these conditions, there is a gradient between the outlet and the exhaust-gas inlet, such that the condensate can flow away from the outlet and to the drain. Thus, in proper use, the outlet is above the drain.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.